Microsoft and Apple began working together on Bing two years ago, when Apple added Bing to its list of search engines for its Safari browser.

Once that project was done, Microsoft and Apple felt so good about the results that they decided to tackle Bing integration in iOS 7, Derrick Connell, Microsoft's VP of program management for Bing, said Monday in an interview with Tom Warren of The Verge.

"Managing the Windows work and the Apple work in some ways was not easy, but doable on our platform," Connell said in the interview.

One challenge was that Apple execs didn't have much experience with Bing, so there were questions about whether it could work well with Siri.

But after immersing themselves in Bing, the Apple execs decided to go ahead with the project, Connell said in the interview.

"I think a lot of the execs at Apple switched over to Bing for a period just to see if they could get the full experience of using Bing," Connell told Warren.

As recently as 2010, the Microsoft and Apple's relationship wasn't that great.